The present invention relates to a unit for controlling a brushless motor and an air conditioner which is driven by a brushless motor.
Recently, energy-saving has been strongly urged to prevent global warming. This is particularly applicable to air conditioners. For this purpose, and to provide high-efficiency operations in recent air conditioners have employed a method of using brushless motors to run a compressor and a fan in the outdoor unit of each air conditioning system. This conventional method of using brushless motors has been disclosed in Japanese Patent laid-open Publication No. 8-35713 (1996), and an example of this conventional approach is illustrated in FIG. 11.
Referring to FIG. 11, microcomputer 8 receives signals from a position detecting circuit 9 of a brushless motor 5 for a compressor and a position detecting circuit 10 of a brushless motor 7 for a fan, estimates the pole position of the rotor of each brushless motor, generates signals to drive switching elements of inverters 4 and 6, causes the switching elements to turn on, according to the pole positions of each brushless motor, and thus drives the respective brushless motors at various speeds. The microcomputer also controls a d.c. voltage to a preset value which is determined by the load and revolutions per minute of the compressor motor and generates a signal to drive a switching element 31 of a boosting chopper 3 to shape the waveform of a current fed to a rectifying circuit 2 (to form sine waves), to eliminate higher harmonic components in the input current, and to improve the power factors.
The above processing enables the brushless motor for the compressor and the brushless motor for the fan to be run at various speeds by the inverters. This can make the air conditioner more efficient.
The above-referenced publication has disclosed that the microcomputer 8 has a function of controlling the brushless motor 5 for the compressor, the brushless motor 7 for the fan, and the boosting chopper 3. However, no reference has been made therein to the fact that the microcomputer has to control the whole outdoor unit of the air conditioner. In other words, the microcomputer 8 is required to control all elements of the outdoor unit, including coolant valves, relays, etc. in addition to control for the two inverters 4 and 6 and the brushless motors 5 and 7. Therefore, the microcomputer 8 must perform various operations in a time sharing manner according to the control cycles of the respective units. This makes the software of the microcomputer 8 very complicated. Further, the software for the microcomputer 8 must be changed greatly if steps are taken to improve the cooling cycle or to change the sequences of the air conditioner, which increases the steps for functional changes.
With the above problems in mind, the air conditioner in accordance with the present invention contains a microcomputer for controlling two brushless motors in the outdoor unit and a microcomputer for controlling the whole outdoor unit. This can separate control of the brushless motors and inverters from control of the whole outdoor unit and prevent the software for each microcomputer from being complicated. The cooling cycles and sequences can be changed merely by changing the content of software for the microcomputer to control the whole outdoor unit.
Further, the microcomputer to control brushless motors in accordance with the present invention is designed to collectively fetch position detecting signals from the two brushless motors and estimate the positions of their rotor poles, which suppresses the increase of the load of the microcomputer which controls the brushless motors.